GAAS ALGAAS QUANTUM-WELL INFRARED PHOTODETECTOR ARRAYS FOR THERMAL IMAGING APPLICATIONS/

The performance of GaAs/AlGaAs multiple quantum well infrared detector s is studied theoretically and experimentally, with special emphasis o n 8-12 mu m thermal imaging applications. The dependence of detector p erformance on various factors like light coupling configurations (one and two dimensional reflection gratings or 45 degrees polished edge), detector temperature, response wavelength and quantum well doping dens ity is dealt with. An absorption quantum efficiency of 87% is demonstr ated using a crossed grating and a waveguide (CGW). It is also found t hat an optimised 341 mu m x 34 mu m detector (a detector size suitable for large staring arrays, i.e. 256 x 256 or larger) with 9.0 mu m cut -off wavelength, f# = 2 optics and 70% optical transmission reaches ba ckground limited operation at 74K detector temperature. The potential of making highly uniform staring arrays utilising the mature GaAs mate rial and processing technology is demonstrated by uniformity measureme nts of detector dark current. The experiments show that a metalorganic vapour phase epitaxy (MOVPE) grown structure can have a dark current standard deviation to mean value ratio over a 10mm long linear detecto r array of less than 2%. The staring array performance in terms of noi se equivalent temperature difference (temporal NETD) is calculated to NETD < 20mK at 77K detector temperature and NETD < 10 mK at 70K detect or temperature.